Candida albicans is the most important human fungal pathogen, and the incidence of disseminated candidal infection is continuing to rise. This fungus is intractable to genetic and molecular approaches due to its diploid state and lack of a known sexual cycle. Nevertheless, strains with mutations in targeted genes, which affect virulence, were constructed recently, These strains are isogeneic to a clinical isolate parent strain, with which they can be compared. So far, comparisons have consisted of studies of growth characteristics on solid and liquid media, as well as injection into animals and comparisons of animal survival. In order to understand how mutations in certain genes affect Candida's ability to disseminate in the host, cell culture models for three key tissues with which Candida interacts during dissemination will be established. Intestinal epithelial cell lines will be used to represent the mucosal barrier, macrophages to represent host phagocytes, and endothelial cells to represent the blood vessel wall barrier. Existing Candida mutant strains will be used to establish these cell lines as model systems of host-fungus interaction. The next step will be to identify Candida genes that are involved in this interaction, by established procedures for isolating differentially expressed genes. These genes will then be studied in Candida and the effect of their deletion of the host- fungus interaction will be studied in the cell culture models.